This invention relates to automotive ventilation systems in general, and specifically to such a system which uses a pair of in series blowers to reduce system noise.
Typical vehicle bodies have what may be termed an interior or cabin space within which driver and passengers sit, and within which it is necessary to provide constant ventilation air flow and, preferably, to temper the air flow, as well. The cabin space is broadly comprised by a front bulkhead (structure such as instrument panels, etc, that wall off the engine compartment), a roof, floor, and rear bulkhead, defined generally as structure that walls off the rear seating area from the trunk. Conventional vehicle heating, air conditioning and ventilation systems (HVAC systems) consist basically of a box like housing, containing blower, heat exchangers, and air valves through which air is either pulled from outside the vehicle and blown into the cabin space, slightly pressurizing it, or recirculated within the vehicle.
In the xe2x80x9cfreshxe2x80x9d or outside air mode, the outside air that is pulled in by the blower is blown toward the rear of the cabin space and eventually, under the slight cabin pressure, flow through rear vents into the trunk space and passively exhausted back to the outside through conventional, passively acting vent valves. These are typically a one way acting rubber flap that can be blown slightly outward under pressure, but which close to prevent reverse flow. In recirculation mode, recirculated cabin air is pulled back up through a large under dash opening and into the HVAC housing before being blown back out. Blower noise is a concern with such a system. The single blower, since it provides all of the air moving power both for air introduction and air exhaustion, must turn at high RPMs, and noise goes up severely with higher blower speeds. Another cause of noise is the large under dash opening through which recirculated air is pulled. It represents a very direct blower noise path from the HVAC housing into the cabin space.
Multi blower ventilation systems are known. More than one blower would not, intuitively, seem to provide a noise reduction, and just the opposite in fact. Such systems do appear to be primarily directed at issues other than noise, and primarily at a desire to separate the fresh air introduction and interior air recirculation functions by providing a blower and ductwork dedicated independently to each function. For example, a farm tractor ventilation system disclosed in U.S. Pat. No. 4,344,356 shows a two blower system in which the two blowers operate in parallel to separate the fresh air introduction and in side air recirculation functions . The primary purpose of the system is to create a constant and high interior cabin pressurization to assure that exterior dust is not pulled in, a concern that is more pronounced with agricultural and earth moving equipment.
The subject invention provides a ventilation system directed primarily at on road vehicles in which a pair of blowers operate cooperatively and in series, rather than in parallel, to both create a front to rear, outside air ventilating flow, and to create an interior air, recirculating air flow, with reduced blower noise in each case, despite the extra blower.
In the embodiment disclosed, two blower housings are incorporated, a ventilation housing at the front of the cabin space and an exhaust housing at the rear. A continuous duct runs from the exhaust housing back to the ventilation housing, taking the place of the under dash opening into the ventilation housing for recirculated air. The ventilation housing has a valved blower which, in a ventilation mode, pulls in outside air into the cabin space, or, in a recirculation mode, pulls air from the front of the common duct. The exhaust housing has a blower which, in an exhaust mode, pulls in cabin air and exhausts it, under power, outside the vehicle, or instead blows air into rear of the common duct and back toward the ventilation housing.
The two blowers thus work in series, when each is in its ventilation mode, to pull outside air in at the front of the cabin space and exhaust it, actively, through the rear of the cabin space. The same air flow can be achieved with each blower turning at significantly less speed than a conventional single blower.
The two blowers also operate in series in recirculation mode, but recirculate interior cabin air from the front of the cabin space, to the rear, and then back to the front through the common duct. In addition, since, in recirculation mode, the return leg of the flow is through a continuous, closed common duct, there is no direct, open noise path either blower to the cabin space. Both the reduced fan speed and the closed duct serve to reduce perceived blower noise within the cabin space.